Controls for refrigeration systems having air cooled condensers



Deu, 6 1%@ c. N. HEARD 312%?429 CONTROLS FOR REFRIGERATION SYSTEMS HAVING AR COOLED CONDENSERS Filed June 29, 1965 CHARLES N. BEARD, @Y m15, /Zpmw ATTORNEY United States Patent O 3,289,429 CONTROLS FOR REFREGERATlGN SYSTEMS HAVHNG AIR COLED CONDENSERS Charles N. Beard, Staunton, Va., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed .lune 29, 1965, Ser. No. 467,832 3 Claims. (Cl. 62-183) ates, and shortly thereafter will raise the suction pressure above that at which the low pressure cut-out operates. As a result, the low pressure cut-out will cycle the compressor on and oft if provided with an automatic reset, and will require resetting if provided with a manual reset.

This problem is well known, and there are available, electrical time delay devices for delaying the tripping action ot' low pressure cut-outs. Such devices are complicated and expensive.

For some duties, it is usual to operate refrigeration systems having air cooled condensers, when used for the conditioning of air, at such low outdoor temperatures that the condensing pressure is too low to operate properly the refrigerant expansion devices used, requiring additional means to increase the condensing pressure. The U.S. patent of R. S. Stewart, No. 3,112,620, discloses a control system in which an outdoor thermostat is used to reduce the number of fans operating to move outdoor air over a condenser coil for preventing excessive decreases in condensing pressure.

This invention provides in a single, inexpensive, control circuit, a thermostat responsive to liquid temperature in such a system, which maintains a switch shunted across the usual low pressure cut-out switch, closed until the liquid reaches a predetermined temperature, preventing cycling of the compressor, and in which the same thermostat controls the number of fans moving outdoor air over a condenser coil for maintaining condensing pressure.

Objects of this invention are to simplify and reduce the costs of controls for refrigeration systems having air cooled condensers.

This invention will now be described with reference to the annexed drawing which is a diagrammatic view of a refrigeration system embodying this invention.

A refrigerant compressor C, driven by .an electric motor CM is connected by discharge gas tube 10 to one end of a condenser coil 11, the other end of which is connected by liquid tube 12 containing a conventional expansion valve 13, to one end of evaporator coil 14. The other end of the evaporator coil 14 is connected by suction gas tube 15 containing a conventional low pressure cut-out 16, to the suction side of the compressor C.

The condenser coil 11 has air guiding, end sheets 16 and 17, and has an intermediate air guiding sheet 18. A fan 19 driven by an electric motor 20 is located between the sheets 16 and 18, and fans 21 and 22 driven by electric motors 23 and 24 respectively, are located between the sheets 18 and 17. The sheet 18 prevents recirculation of air when the fan 19 is turned off, and when the fans 21 and 22 are turned of.

The low pressure cut-out 16 has a normally closed ICC switch 25 which opens when the suction gas pressure is below, for example, 30 p.s.i., and which is connected in series with energizing winding 26 of compressor motor starter CMS, and switch 28 of space thermostat T1 to electric supply lines L1 and L2. The starter CMS has a switch 29 which is closed when the winding 26 is energized, and which is connected in series with the compressor motor CM to the supply lines L1 and L2. Shunted across the switch 25 by wires 30 is a normally closed switch 31 of thermostat T2 which is in heat exchange contact with the liquid tube 12. The switch 31 remains closed until the temperature of the liquid within the tube 12 increases above, for example, F. The thermostat T2 has a normally open switch 34 connected by Wire 35 to the line L2, and by wire 36 to one end of energizing winding 37 of starter 38 of the fan motor 20. The other end of the winding 37 is connected by wire 49 to the line L1. The fan motor starter 38 has a switch 39 which is closed when the winding 37 is energized by the closing of the switch 34, and connects the fan motor 20 by the wire 49 to the line L1 and by wire 50 to the line L2?. The switch 34 closes when the switch 31 opens. The thermostat T2 has a normally open switch 40 which is connected by the wire 35 to the line L2 and by wire 41 to one end of energizing winding 42 of fan motor starter 43. The other end of the winding 42 is connected by the wire 43 to the line L1. The fan motor starter 43 has a switch 44 which closes when the Winding 42 is energized, and connects the fan motors 23 and 24 through the wire 49 to the line L1 and through the wire 50 to the line L2. The switch 40 closes when the temperature of the liquid within the tube 12 increases, for example to 120 F. When the winding 42 is energized by the closing of the switch 40, the fan motors 23 and 24 are energized by the closing of the switch 44, and start the fans 21 and 22.

Operation When the thermostat T1 calls for cooling, its switch 2S closes and connects through the closed switch 25 of the low pressure cut-out 16, Shunted by the closed switch 31 of the thermostat T2, the energizing winding 26 of the compressor motor. starter CMS to the supply lines L1 and L2, energizing the starter CMS which closes its switch 29 connecting the compressor motor CM to the supply lines. The compressor C is started, and supplies discharge gas through the tube 10 into the condenser coil 11. Liquid from the coil 11 ilows through the tube 12 and expansion valve 13 into the evaporator coil 14. Gas from the coil 14 flows through the suction gas tube 15 and the cut-out 16 to the suction side of the compressor C.

It the compressor has been turned ott for several hours, and the outdoor temperature to which the condenser coil 11 is exposed is as low, for example, as 55 F., the pressure within the suction gas tube 15 may be 60 p.s.i. so that the switch 25 of the low pressure cut-out 16 is closed. About ten seconds after the compressor is started by the thermostat T1, it pulls down the suction gas pressure to about 15 p.s.i. The switch 25 opens at this time but cannot deenergize the compressor motor starter CMS since the closed switch 31 ofthe thermostat T2 is Shunted across the switch 25. Thus, recycling of the compressor when it is restarted is prevented.

At outdoor temperatures below 55 F., the temperature of the liquid within the tube 12 is below 110 F., and the switches 34 and 40 of the thermostat T2 are open. The fan motor starters 38 and 43 are deenergized, and the fans 19, 21 and 22 are turned oif so as to increase condensing pressure.

When the outdoor temperature increases above 55 F., the temperature of the liquid within the tube 12 increases above 110 F., the switch 34 of the thermostat T2 closes, and the fan motor starter 38 is energized. The latter 3 closes its switch 39, starting the fan motor Ztl and its fan 19. The switch 31 of the thermostat T2 opens at this time, removing the shunt across the switch 25 of the low pressure cut-out 16.

When the outdoor temperature increases above 65 F., the temperature of the liquid within the tube 12 increases above 120 F., the switch 40 of the thermostat T2 closes, and the fan motor starter 43 is energized. The latter closes its switch 44, energizing the fan motors 23 and 24, starting the fans 21 and 22, with all three of the condenser cooling fans in operation.

What is claimed is:

1. In a refrigeration system comprising a compressor, an air cooled condenser coil, a discharge gas tube connecting said coil to said compressor, an expansion device, a liquid tube connecting said coil to said device, an evaporator coil connected to said device, and a suction gas tube connecting said evaporator coil to said compressor, said suction gas tube containing a low pressure cut-out having a switch which opens at abnormally low suction gas pressures, said compressor having an electric driving motor, said motor having a starter relay, electric supply connections, said relay having a switch for connecting said motor to said connections, a control switch, and means connecting said control switch, said switch of said cut-out and said relay in series to said connections, the combination of a thermostat responsive to the temperature of the liquid within said liquid tube, said thermostat having a switch which opens when the temperature of the liquid within said liquid tube decreases to a predetermined ternperature, and means connecting said switch of said thermostat across said switch of said cut-out.

2. The invention claimed in claim 1 in which said thermostat has a second switch whichy closes when said trst mentioned switch of said thermostat opens, in which there is provided a fan for moving air over said condenser coil, in which said fan has an electric driving motor, in which said motor of said fan has a starter relay, in which said starter relay of said fan motor has a switch for connecting said motor of said fan to said connections, and in which means including said second switch is provided for connecting said starter relay of said fan motor to said connections.

3. The invention claimed in claim 2 in which said thermostat has a third switch which closes when the temperature of the liquid within said liquid tube increases to a predetermined temperature above said rst mentioned temperature, in which there is provided a second fan for moving air over said condenser coil, in which said second fan has a second electric driving motor, in which said second starter has a second starter relay, in which said second starter relay has a second switch for connecting said second motor to said connections, and in which means including said third switch is provided for connecting said second starter relay to said connections.

References Cited by the Examiner UNITED STATES PATENTS 3,112,620 12/1963 Stewart 62-183 3,138,941 6/1964 Jensen 62-183 3,191,399 6/1965 Stewart 62-183 X MEYER PERLIN, Primary Examiner. 

1. IN A REFRIGERATION SYSTEM COMPRISING A COMPRESSOR, AN AIR COOLED CONDENSER COIL, A DISCHARGE GAS TUBE CONNECTING SAID COIL TO SAID COMPRESSOR, AND EXPANSION DEVICE, A LIQUID TUBE CONNECTING SAID COIL TO SAID DEVICE, AND EVAPORATOR COIL CONNECTED TO SAID DEVICE, AND A SUCTION GAS TUBE CONNECTING SAID EVAPORATOR COIL TO SAID COMPRESSOR, SAID SUCTION GAS TUBE CONTAINING A LOW PRESSURE CUT-OFF HAVING A SWITCH WHICH OPENS AT ABNORMALLY LOW SUCTION GAS PRESSURES, SAID COMPRESSOR HAVING AN ELECTRIC DRIVING MOTOR, SAID MOTOR HAVING A STARTER RELAY , ELECTRIC SUPPLY CONNECTION, SAID RELAY HAVING A SWITCH FOR CONNECTING SAID MOTOR TO SAID CONNECTIONS, A CONTROL SWITCH, AND MEANS CONNECTING SAID CONTROL SWITCH, SAID SWITCH OF SAID CUT-OUT AND SAID RELAY IN SERIES TO SAID CONNECTIONS, THE COMBINA- 